The invention relates to pneumatic vehicle tires comprising a multi-ply carcass, which extends between two bead rings having associated bead apexes, a belt arrangement provided between the carcass plies and a tread strip and also rubber reinforcing plies arranged in the side wall regions, which take on a supporting function with a deflated tire.
Vehicle tires of this kind are known, for example, from U.S. Pat. No. 5,368,082. It is possible by means of such tires to also cover even fairly long distances at a suitable speed with a deflated tire in the event of a flat, before the tire has to be repaired or changed. Such tires accordingly increase safety in the event of a flat and allow the next repair workshop to be reached without problem so that unwanted tire changes, which can also be dangerous on very busy roads, can be avoided.
It is the object of the present invention to design a pneumatic vehicle tire of the kind initially mentioned such that a high mileage at a sufficiently high speed is also made possible in the deflated state, that the stiffening rubber layers provided in the side walls do not irritatingly impair the driving comfort of the tire operated at normal pressure and that the tire weight remains as low as possible.
This object is essentially satisfied in accordance with the invention by a first rubber reinforcing ply being arranged radially within a first carcass ply and a second rubber reinforcing ply being arranged between the first carcass ply and a second carcass ply, by mutually displaced ends of the two rubber reinforcing plies (4, 5) extending, starting from the bead apex region, up to and beneath the edge region of the belt ply, and by the two rubber plies having in particular a different height in the radial direction and pronouncedly different thicknesses over the height of the side wall.
Both rubber reinforcing plies and any bead apex provided and/or a bead apex region formed of one rubber reinforcing ply preferably consist of the same rubber mixture.
Optimum values are achieved with regard to the long-term running properties of deflated tires on the basis of the selection of the rubber mixture, the thickness profile of the rubber reinforcing plies and the respective curing times of these rubber reinforcing plies, which differ in dependence on the position of the rubber reinforcing plies in the tires, in particular when the modulus of elasticity (E*) of the rubber reinforcing plies and also of the bead apex are the same as or greater than 9 MPa when measured at 70xc2x0 C. and the tanxcex4 is the same as or smaller than 0.03 (measured by means of xe2x80x9cEPLEXORxe2x80x9d, 10 Hz, 10% prestress and 1% DSA). The hardness IRHD of these rubber reinforcing plies and of the bead apex should be the same as or greater than 80 when measured at room temperature. The measurement of the IRDH (international rubber hardness degree) is made analog to the Shore hardness measurement, but with a spherical measuring tip. The measurement or test is carried out in accordance with DIN 53519, whereby the so-called micro-hardness is determined, since small samples are measured which are taken from the respective tire.
The rubber reinforcing plies and the bead apexes or the bead apex regions integrally formed with a rubber reinforcing ply are preferably made of a rubber mixture which consists of a polymer mix of natural rubber (NR)/ isoprene rubber (IR) and butadiene rubber (BR), with at least 50 parts by weight per 100 parts by weight of rubber (phr) NR/IR being contained in this polymer mix, a carbon black content of 50 to 60 phr, preferably of fast sprayable FEF carbon black, and of 5 to 8 phr zinc oxide, 2 phr stearic acid, 1.5 phr of aging protection agent and one or more phr of vulcanization accelerator and sulfur (preferably 4 to 5 phr) in order to keep the loss properties of the mixture low.
In the event that the radially inner end of the outer rubber reinforcing ply is simultaneously formed as the bead apex, it is provided that when measured in the region of the maximum bead thickness (side wall height W), the thickness of the inner rubber reinforcing ply amounts to approximately 4.4 mm and the thickness of the outer rubber reinforcing ply amounts to approximately 8.7 mm, with a tolerance of xc2x10.5 mm applying to all measured values.
Further advantageous embodiments of the invention are given in the dependent claims.